Migration control station Scorff

The migratory fish monitoring station is located on the lower reaches of the River Scorff, at the edge of the estuary, just beyond the tidal influence zone, at Pont Scorff on the site of the Moulin des Princes. The site is open to the public; fish trapping activities take place throughout the year. This station enables the capture of migratory fish both as they swim upstream and downstream. The main species caught are salmon, trout, eels, shad and lampreys.

Trapping

The migratory fish monitoring station has been in operation since 1994 and is situated downstream of the Scorff, approximately 10 km from Lorient harbour (14 km from the coastline). It is located on the inlet channel of the Moulin des Princes in Pont-Scorff. The station comprises two trapping systems, one for upstream and one for downstream. A rocky breakwater has been installed to guide the fish towards the station, but it only allows for partial capture, which means the effectiveness of the traps must be assessed.

The various parameters recorded during trapping fall into three categories: environmental, technical and biological.

• Date, general weather conditions; rainfall (measured using the rain gauge at the Moulin des Princes).
• Trap in which the fish was caught, time of recording.
• Species; type for migrating juveniles (smolt, silver, adult, etc.), sex (mainly for adults), size, weight;  observations on the general condition of the fish, scale sampling depending on species and size (placed in a numbered paper bag), additional samples taken for experimental purposes, type of marking observed and applied  (Upstream trap: all salmon are marked with Alcian blue on the abdomen).

The number of fish migrating upstream and downstream is estimated using capture-mark-recapture surveys, which enable the trap’s efficiency to be assessed.

Depending on the species, age can be estimated using the Petersen method (size distribution histogram), scalimetry or individual tagging (Pit Tag).

The downstream fish trap

This trap captures fish swimming downstream. Some of the fish are initially guided towards the mill’s intake. Upon reaching the control station, the fish encounter a fixed grid fitted with a fish-removal device. They must take a side overflow and enter a cage.

The upstream fish trap

This trap captures fish migrating upstream. The fish are first guided by a rockfill of boulders placed in the Scorff towards the branch of the Moulin des Princes outlet channel, where the trap is located.

The fish enter the cage via a funnel and cannot find their way out (pot trap system).

Main species monitored 

	Shad Monitoring of shad populations since 1994
	Eels Monitoring of eels populations since 1994
	Lampreys Monitoring of lampreys populations since 1994
	Mullets Monitoring of mullets populations since 1994
	Salmon Monitoring of salmon populations since 1994	See report
	Sea trout Monitoring of sea trout populations since 1994